1. Field of the Invention
The present invention relates to light directing sheeting, films, panels and light control devices incorporating same. More particularly, this invention relates to light directing sheets, panels and films capable of redirecting off-normal light rays at relatively high bend angles, including bend angles exceeding 90 degrees. This invention further relates to light directing sheet-form materials for the use in daylight-harvesting glazing for enhanced natural illumination of building interiors or other types of enclosed structures. It also further relates to window coverings, skylights, artificial light control devices and daylight control devices.
2. Description of Background Art
Various optical films and panels used to redirect light often incorporate prismatic surface microstructures such as linear prism arrays and the like. Such prismatic microstructures typically include surfaces that are not parallel to the prevailing plane of the film or panel and can thus redirect light by a prescribed angle by means of refraction or total internal reflection (TIR).
However, the bend angles that can be achieved using prismatic microstructures are limited and typically are below 60 degrees in practice. Additionally, the exposed micro-prismatic surfaces are prone to soiling and damage. Lamination of such surfaces onto other surfaces without impairing the optical performance of the device is problematic due to the unavoidable air gaps between surface microstructures. Furthermore, micro-prismatic surfaces redirect not only the off-normal rays but also rays that have normal incidence thus impeding the view of objects behind such surfaces.
Accordingly, practical light directing sheet materials are needed that could be implemented with smooth external surfaces and that can be configured to bend light by larger angles. Furthermore, practical light harvesting and light control devices and systems that employ such light directing sheet materials are also needed. These needs and others are met within the present invention, which provides an improved sheet-form structure for redirecting off-normal light rays at high bend angles without the need of outer surface texturing and also provides a method of making the same. The improved sheet-form structure employs internal TIR surfaces to efficiently redirect light and can also be made thin and flexible, finding utility in various light control devices and systems.